Multi-stage flash evaporators



July 27, 1965 H. R. LAWRANCE 4 Sheets-Sheet 1 Filed May 20, 1963 INVENTOR. i HAROLD RICHARD July 27, 1965 H. R. LAWRANCE 3,197,387

MULTI-STAGE FLASH EVAPORATORS Filed May 20, 1965 4 Sheets-Sheet 2 & j:

Arron/5r July 27, 1965 Filed May 20, 1963 IQIOIQ'I 4 Sheets-Sheet 3 l l I I l l I l I Ill INVENTOR. HAROLD RICHARD LAM RANGE BY 2 5M AT 7' ORIVE V July 27, H. R. LAWRANCE MULTI-STAGE FLASH EVAPORATORS Filed May 20, 1963 i 4 Sheets-Sheet 4 IN VENTOR.

HAROLD RICHARD LAWRA/VCE BY 5w ATTORNEY United States Patent 0 3,17,3S7 l'i IUL'II-ETAGE FLASH EVAIQRATORS Harold Richard Lawrance, Swarthmore, Pa, assignor to Baidwin-Lima-Hamilton Corporation, Philadelphia, Pa, a corporation of Pennsylvania Filed I i lay 2t 1963, Ser. No. 281,734 2% Claims. (Cl. 2tl2173) In general, this invention relates to a new and improved flash evaporator construction for use in distilling sea water and the like and, more particularly, to a multistage flash evaporator which allows the transfer of saturated liquid from stage to stage with a minimum pressure drop while maintaining equilibrium conditions.

Many prior forms and constructions of flash evaporators have been provided making use of various types of feed water devices, that is, devices through which the sea water brine or other liquid to be distilled is introduced into the particular flash evaporator stage. In all flash evaporators, of course, the liquid to be distilled is introduced through a feed water device into a chamber having an internal chamber pressure below the saturation pressure of the liquid at the particular temperature of the liquid whereby a certain portion of the liquid flashes into vapor with such vapor subsequently being condensed to produce the desired distillate.

Gne such flash evaporator is described in US. patent application Serial No. 139,411, filed September 20, 1961, now U.S. Patent 3,160,571, for Evaporator Construction by Stewart F. Mulford and Darrell G. Durst. In this last-mentioned construction, flashing took place as the liquid entered each stage from the next preceding stage. That is, the liquid expanded from an opening in the wall of the next preceding stage into a wide chamber creating a liquid-vapor mixture which was forced through a riser box and passed through an aggregate bed wherein the liquid was separated from the vapor. Such a unit had to be made extremely wide in order to increase the flashing area and thus increase the capacity of the evaporator unit. Further, it was necessary to maintain high pressure drops in order to pass the liquid-vapor mixture through the aggregate beds.

In the present invention, the separation of the liquid from the vapor is achieved by flasmng the liquid only in the riser chamber causing a gas lift effect in the riser chamber and lifting the liquid-vapor mixture over the side walls of the riser chamber to allow it to free fall into a separate part of the evaporator chamber. During the free fall, there would be no hydrostatic pressures on the liquid-vapor mixture and the vapor could completely separate from the liquid during free fall. Since, where a high degree of purity is required in the final distillate, it was necessary to pass the vapors flash from the liquid in each evaporator chamber through a vapor separator or eliminator prior to condensing of these vapors, in the present invention such is accomplished by forcing the vapors to pass through such an eliminator before they can reach the condenser. In this manner, liquid droplets which might be entrained in the vapor are removed, which droplets would normally carry a certain amount of the impurities with the vapor into the final distillate receiver.

In the continued development of flash distillation plants, it is the common goal to produce a distillation plant of the lowest over-all cost, both in original fabrication and construction, as well as in operation thereof.

It is known that a major advance toward the production of an optimum flash distillation plant can be made by improving the feed water device or devices of the present flash distillation plants and it is principally to this end that the improvements of the present invention are directed.

Improvement of the feed water devices for flash distillation plants does not necessarily require that these feed water devices be of a construction having a lower cost than the prior feed water devices, although minimum costs are desirable. By the present invention, it is possible to increase the capacity of the stages of the evaporators by increasing the length of the flash boxes rather than increasing the width or cross sectional area of the tank in which each evaporator stage is mounted. By increasing the length to achieve greater flashing area and, therefore, greater capacity, a large increase in savings has been achieved.

A further factor to be considered is that the evaporator stages must be capable of being utilized under small pressure differential conditions so that equilibrium is possible with a large number of stages.

Further, the heat used up in one part of the flash distillation cycle should be fed back into another part of the flash distillation cycle so as to minimize losses in the cycle and maintain equilibrium conditions.

It is, therefore, the general object of the present invention to provide an improved multi-stage flash evaporator system which eliminates the foregoing problems and incorporates the advantages of the foregoing principles.

It is a primary object of the present invention to provide an improved feed water device construction for flash evaporators which produces a maximum release of vapors within any given flash evaporator stage and a greater proportion and amount than hasbeen heretofore possible in prior art flash evaporators.

It is a further object of the present invention to provide an improved feed water device construction for flash evaporators which accomplishes the maximum elimination of water droplets from the vapors directly within the feed water device.

A still further object of the present-invention is to provide a new and improved multi-stage flash evaporator which is simple in construction and minimizes heat losses throughout the cycle of operation.

Another object of this invention is to provide an improved flash evaporator stage whose flashing area can be increased by elongating the flasher box of the stage.

Finally, it is an object of the present invention to provide an improved multi-stage flash evaporator system which, through increased efhciency, makes possible the production of distillate of a maximum purity at a minimum cost of original fabrication and construction of the flash evaporators as well as the operation thereof.

Other objects will appear hereinafter.

For the purpose of illustrating the invention, there are shown in the drawings forms which are presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIGURE 1 is a partially cut away view of one flash evaporator stage built in accordance with the principles of the present invention.

FIGURE 2 is a cross sectional view of the stage of FIGURE 1 taken along lines 22.

FIGURE 3 is a cross sectional View of the stage of FIGURE 1 taken along lines 33 in FIGURE 2:

FIGURE 4 is a plan view of one of the end walls of one stage of the evaporator of FIGURES 1-3.

FIGURE 5 is a diagrammatic showing of a complete multi-stage flash evaporator system incorporating the flash evaporator stages shown in FIGURES 1-4.

FIGURE 6 is a cross sectional view of one stage of a 3 tandem flash evaporator unit built in accordance with the principles of the present invention.

FIGURE 7 is a cross sectional view of the tandem evaporator unit of FIGURE 6 taken along lines 7- 7 showing it in combination with other similar tandem units.

In FIGURE 1, there is shown a portion of a multistage flash evaporator unit built in accordance with the principles of the present invention and generally designated by the numeral 1%. The apparatus 10 is provided with an outer cylindrical housing 12 within which is positioned a single unit flash evaporator stage 14 which will be described in detail below.

The flash evaporator stage 14 is intermediate an input flash evaporator stage 16 and an output flash evaporator stage 18.

The stage 14 is defined by two circular end walls 29, 22 whose outer periphery is juxtaposed to the inner surface of the cylindrical housing 12. The end walls 2t and 22 have openings therein at points which will be discussed below.

Between each of the flat end walls 20 and 22 is a flash box or riser chamber 24 having spaced parallel walls 26 and 28 extending between the end walls 20 and 22...

The flash box side walls 26 and 28 have bottom edges 30 and 32 respectively defining an open bottom for the flash box 24 and top edges 34 and 36 respectively defining an open top for the flash box 24.

A liquid separating wall 38 is provided between side wall 28 and shell 12. This liquid separating wall is an inclined surface extending from the top edge 36 of side wall 23 adjacent end wall 20 to the bottom edge 32 of wall 28 adjacent end wall 22. A similar liquid separating wall 40 is provided between side wall 26 and shell 12 running from the top edge 34 of wall 26 adjacent end wall 20 to the bottom edge 30 of wall 26 adjacent end wall 22.

The liquid separating wall 38 divides the stage 14 into a first unflashed water compartment 42 below wall 38 and a first flashed water compartment 44 above wall 38. Similarly, wall 40 separates the stage 14 into a second unflashed water compartment 46 below wall 49 and a second flashed water compartment above wall 49. The wall 22 has a first opening 5t} therein defined by the lowermost edge of wall 38, wall 28, shell 12, and a cut out edge 51 parallel to the lowermost edge of wall 33 and perpendicular to wall 28 at a point below the uppermost edge 36 of wall 28. A similar opening is formed in end wall 26 and all other end walls in the multi-stage system.

The end wall 22 has a second opening 52 formed therein defined by the lowermost edge of wall 40, side wall 26, shell 12, and a cut out edge 53 on end wall 22 perpendicular to side wall 26 below the top edge 34 thereof and parallel to the bottom edge of wall 40.

Thus, it can be seen that if the liquid level in the flashed water compartments 44- and 48 is above the edges 51 and 53, the space above the water in the compartments 4 and .8 will be isolated from both the input stage 16 and the output stage 18.

Further, there is provided above the riser chamber 24 a pair of curved liquid-vapor deflectors 54 and 56 which act to deflect the liquid-vapor mixture forced upwardly through the riser chamber 24 so that it will fall freely into the flashed water chambers 44 and 43 and vapors mixed with the liquid will be freed and separated from the flashed liquid. These vapors will pass through suitable vapor-liquid separators 5S and 60 running the length of the evaporator between end walls 20 and 22 formed of a labyrinth mesh which will catch liquid droplets therein and allow the vapor to pass to a condenser assembly 62 located above the deflectors S4 and 56.

The condenser assembly 62 consists of condenser tubes 64 through which cooling liquid brine passes and around which are placed suitable cooling fins 66 on which the vapors will condense. The condensed vapors will drop as liquid into a distillate pan 63 located immediately below the condenser unit 62 which will collect the dis tillate and pass the so-collected water out through a distillate pipe '75) where it may be received in a product storage tank.

The operation of a single stage of the multi-stage flash evaporator system of the present invention is as follows:

First, hot brine enters the unflasiied compartments 42 and 46 through the openings 56' and 52' in the end plate 2% from the prior input stage 16. This liquid has previously been flashed in the stage 16 and has a high density as it passes through the openings 5'6" and 52'. However, the high density liquid will not flash as it passes the end wall 2% as there is little change in area between the compartments 44 and $3 at the lower ends of separating walls 33' and ii. This hot liquid brine enters the riser chamber 24 by passing under the bottom edges 30 and 32 of side walls and 28, and flows upward under the influence of the differential pressure existing between the areas containing hi h density untlashed and low density flashed brine. As the liquid rises in riser chamber 24, the hydrostatic effects on the liquid are reduced due to the slightly lower pressure in chamber 14 than in input chamber 16. When this occurs, boiling begins. The boiling moisture density of the liquid in riser chamber 24- is much less than the density of the unflashed water which is maintained at a level slightly below the top edges 3 and 36' of the previous stage 16. The density difference between the brine flowing through the flash box 24 and the mixture flowing to it gives rise to an unbalanced force substantially increasing the pressure differential for flow. This brine-steam mixture in the riser chamber 2 is forced upward over the top edges 34 and 36 against the deflectors 54 and 56 to fall freely into the flashed water compartments 44 and 48. During this free fall, there are no hydrostatic effects on the liquid-vapor mixture and the vapor can freely separate from the liquid and rise upwardly toward the separators 58 and 69. The steam passes through the separators 58 and 60 to the cooled condenser tubes to be collected in the distillate pan 63.

The liquid brine falls back to the brine level outside of the flash box 24-. This liquid then flows lengthwise along the shell 26 through the increasing area between the brine level and the sloped walls 33 and 49. Thus, as the liquid flow rate is increased with respect to the length of the shell, the flow area increases which will maintain a substantially constant velocity. As the brine flows through the opening 50 into the flash box of the next succeeding stage 13, the flow rate is reducedwith respect to the shell length and flow area is reduced by the liqiud separating wall of the next succeeding chamber.

Thus, at the end of the stage, the water flows under the influence of gravity through the partition wall 22 separating adjacent stages and under the sloped plate wall located in the downstream compartment in order that the whole cycle might again be repeated.

It should be understood that no flashing occurs as the liquid flows through the openings 5%, 52 and S0, 52 in the end walls 22 and 2t and pressure losses are minimized by maintaining a maximum density at this point. As the liquid rises in the box-like riser chamber 24, the hydrostatic forces are reduced. The liquid becomes superheated as a result and flashes, thereby reducing the density which quickly reduces the hydrostatic head and results in further flashing. The flashing is substantially complete when the liquid reaches the top edges 34 and 36 of the riser chamber 24 and hydrostatic eflects cease to exist. Thus, the maximum possible heat release is ob- 'tained.

As it will be noted, by utilizing this cascading effect of the liquid-gas mixture in the riser chamber, only a small pressure differential is necessary between each stage to obtain flashing. The important feature is the lifting of the gas-liquid mixture and the dropping thereof into the chambers 44 and 48 so that maximum separation of liquid from vapor can be achieved. This maximum separation occurs as there is no hydrostatic effect on the mixture during free fall. Since the amount of flash evaporation depends upon the area over which flash evaporation occurs, the area can be increased by merely lengthening the riser chamber 24 and increasing the length of the entire stage 14.

An understanding of the operation of the unit of FIG- URES 14 in a multi-stage flash evaporator system can be seen in the diagrammatic presentation of FIGURE 5. In FIGURE 5, the system of the present invention has been generally designated by the numeral 72. This system includes thirty flash evaporator stages S1530, each substantially identical to the stage 14 discussed in FIG- URES 14.

In FIGURE 5, the stage S1 is shown with an input conduit 74 for reeciving sea water to be distilled. This sea water or brine is passed through the condenser tubes 64 and used as the coolant. For example, the input sea water could be at 80 F. The first stage S1 also releases brine through an output conduit 76 at approximately 90 F. in order to maintain equilibrium in the system. This will be more fully described below.

The input brine is also mixed with brine already utilized in the process to raise its temperature to approximately 100 F. before passing through the condenser tubes 64. When the brine passes out of the stage S1 through the condenser tubes 64, it passes through the output conduit C1 into the condenser tubes 64 of the next stage 52. Each stage has its own output condenser tube C2430. The brine in the condenser tubes 64 picks up the heat released during the flash evaporation process in each stage S1S30. This temperature gain is between 3 and 3 /2 J.- Thus, in thirty stages, the temperature of the brine in conduits Cit-C30 will have been raised rorn100 F. to approximately 200 F.

The output conduit C30 for stage S30 is also the input B30 for the feed water device of stage 330. In stage S30, F. is added to the temperature of the brine in conduit B30 through an input conduit 78 which raises the temperature thereof. In order to keep thermal equilibrium for the entire multi-stage evaporator, it is necessary that the 10' increase placed in the last stage S30 be removed from the system. This was done through conduit 76 discussed previously. Conduit B30 is symbolic of liquid entering through openings 50' and 52 in end wall considering stage S as equivalent to stage 14 in FIG- URES 1-4.

Since the brine entering stage S30 in conduit B30 is hotter than the brine entering through condenser tubes C29, the vapor will condense on the fins 65 to be received by the distillate pan 68. It will be understood that the distillate could be individually taken from each stage S1- S30 or the distillate could be passed down the system in the manner shown in FIGURES 6 and 7 so as to retain its heat in the system and maximize equilibrium conditions.

The brine from stage S29 which would pass through openings 50 and 52 in wall 22 into the next succeeding stage 18 (S28) is symbolically shown by conduit 1323.

Considering that stage S30 was brought up to saturation conditions, each stage down the line will also be at saturation conditions if equilibrium is achieved in each stage. Further, the temperature differential will be maintained in this manner between the brine flowing through the condenser tubes 64 and the brine entering below liquid separating walls 38 and 40. The output conduit 76 of stage S1 is mixed with the input through conduit 74 to maintain the input temperature constant. Suitable valves may be provided to vary the concentrations of input brine versus flashed brine.

In order to start the system in operation, conduit 76 is shut 011 and brine is entered through conduit 74 which passes the brine through the tubes 64 to stage S30. In

stage S30, this brine is heated, for example, by steam entering through conduit 78 which will then create temperature differential as the output brine pases through the lines B30-B1 raising the temperature in the condenser tubes C1-C30. This continues until the temperature in the last stage S30 reaches its saturation level, and then conduit 76 is opened to prevent further increases in the temperature level or" the system so as to maintain equilibrium conditions.

In FIGURES 6 and 7, there is shown a tandem multistage flash evaporator system which utilizes the principles of the present invention.

In order for the flash evaporator of the present invention to be useful in distilling large quantities of sea water such as ten million gallons per day, its capacity must be such that it can be increased without loss of efliciency. Since the capacity is dependent upon the amount of distillate produced in a given stage, this capacity can be increased by providing a plurality of feed water devices including the flash boxes, such as were shown in FTGURES 1-4, arranged in tandem relation.

In FIGURE 6, there is shown a cross sectional view of one such tandem stage generally designated by the numeral 80. The stage 80 is rectangular in cross section having upright side walls 82 and 84, a top wall 86, and a bottom wall 88.

Adjacent the center of the top wall 86 is a condenser unit 89 having a plurality of condenser tubes 90 running the length of the stage 80. Immediately below the condenser unit 89 is a distillate receiving trough 92 at the center of which is a distillate pipe 94- through which distillate in the trough 92 runs down into a distillate tank 96 located on the bottom wall 88 of the stage 80. The distillate tank 95 has a length at least equal to the length of the stage 80, but is extended to accommodate conduits 156 and 158 as shown in FIGURE 7. The distillate tank 96 has low level openings 98 adjacent the bottom wall 88 at the ends thereof. Additionally, after each opening 98 in the direction of flow of distilled water, there is provided a separating wall 100 extending the width of the opening 98 and slightly higher than the opening 98 to insure proper circulation of distilled water the length of the mult-i-stage unit. The water on the bottom of the distillate tank 96 cannot flow all th way down each stage, but must circulate over the walls 100 in order to go from stage to stage.

The stage 80 includes a plurality of flash boxes 101-106, each extending from end wall 108 to end wall 110 of the stage. The outermost flash boxes 101 and 106 extend upwardly from the bottom wall 88 and have a plurality of openings 11-2 and 114 respectively adjacent the bottom Wall 88. The flash boxes 102405 each extend upwardly to the same height as flash boxes 101 and 106 from the top of the distillate tank 96. The flash boxes 102-105 have similar openings 116, 118, and 12 2 adjacent the top wall of the distillate tank 96.

The top edges of the flash boxes 101-106 are on the same level and each of the flash boxes has a pair of flash deflectors 124 129 respectively extending along the length thereof between the parallel side Walls of the flash box.

Liquid separating walls are provided for each of the flash boxes 101406 extending from the top edge thereof adjacent end wall 100 to the bottom end of the flash box adjacent wall 110. Liquid separating wall 130 extends from the top of the left side wall of flash box 101 to side wall .82 of the housing as and down on an inclined plane to the corner between bottom wall 88 and end wall 110. A second end wall 131 is provided extending between the top edges of the right side wall of flash box 101 and the left side wall of flash box 102 between end walls 108 and 110 in the manner discussed previously. A third liquid separating wall 132 extends between the top edges of flash boxes 102 and 103 and end wall 108 to the bottomedges of flash boxes 102 and 103 adjacent the top wall of distillate tank 96. Still another liq-uid separating wall 134 extends between flash boxes 1G3 and 104 in the manner discussed with respect to separating wall 132. The distillate pipe 94 passes through the wall 134 in the manner shown in FIGURE 6. Liquid separating wall 135 is similar to wall 132 and extends between flash boxes 104 and 105. Liquid separating wall 136 is similar to liquid separating wall 131 and extends between flash boxes 105 and 106. Finally, liquid. separating wall .137 extends between the right side Wall of flash box 106 and side wall 84 of the housing in the same manner as first-mentioned separating wall 130.

It will be noted that the openings 112, 114,116, 118, 120 and 122 in the side walls of the flash boxes 101-106 are all below the liquid separating walls 131-137. These openings 112, 114, 116, 118, 120 and 122 are substitutes for and equivalent to the opening in the bottom wall of the flash box 24 shown in FIGURES 14.

On either side of the condenser 89, there is provided a longitudinally extending separator or eliminator 138 and 140. These separators are utilized to separate the liquid from the vapor before it reaches the condenser unit 89.

In each flash box 101-106, there is provided a butterfly valve 141446 for regulating the pressure in the flash box unit. At the higher temperatures, the valves would be especially useful in limiting th pressure between stages of the unit. At the lower temperatures, the pressure drop between stages is normally less and, therefore, the butterfly valves might be fully open for lower temperatures. These butterfly valves aid is setting up equilibrium conditions for operation and adjusting these conditions for the particular conditions of a distillation cycle.

The end walls 108 and 110 have openings therein similar to the openings 50 and 52 shown in FIGURES 1-4 in that they extend between the bottom edge of each liquid separating wall to a point below the to edge of the flash boxes on either side of the flash box. These are the only openings in the end wall except for the opening 98 previously discussed.

In FIGURE 7, stage 80 is shown in series with two other stages 80' and 80 substantially similar one to an other. In order to limit the length of the unit, the stages, instead of being formed all in line with one another, can be set up in groups such as groups of three shown in FIG- URE 7 with crossover pipes connecting one group of three stages to another. For example, the three group unit shown in FIGURE 7 is one of nine other such units which is connected by an input condenser crossover pipe 148 and an output condenser crossover pipe 150. The brine enters stage 80 through a crossover conduit 152 and leaves the three unit stage by way of a brine output conduit 154 adjacent stage 80". Similarly distillate input is received through distillate tank inlet crossover conduit 156 and leaves through distillate outlet conduit 158 adjacent stage 80".

The operation of each of the flash boxes 101406 is exactly similar to that discussed previously with respect to the single flash box stage shown .in FIGURES 1-4.

The only diflerence lies in the passage of the unflashed brine through the openings 112, 114, 116, 1-18, 120 and '122 rather than through the open bottom wall of the flash boxes. It should be noted that each of the flash box units 101-406 has the same capacity under its asso ciated liquid separating walls as every other flash box by reason of the spacing between flash boxes. Thus, the flow through each stage is exactly equal.

Further, the distillate in the tank 96 has a level higher than the opening 98 adjacent the end walls thereof. Thus, the distillate tank of each stage has pressure and temperature conditions isolated from the next previous or next suceeding stage. The use of the barriers 100 insures that the liquid will not flow along the bottom wall 88, but will insure that all the liquid in any particular distillate tank will pass to the next distillate tank. Further, any of the distillate in tank 56 which is at the saturation level will vaporize and rise through distillate pipe 94 to the condenser 89. In the condenser, it will give up its heat to the condenser coils and return as liquid through the pipe to the tank 96. The distillate will then be removed only at its lowest temperature in the lowest temperature stage of the system. None of the heat in the distillate will be lost to the system as it will be transferred to the condenser tubes in the manner discussed above. In this way, a more eflicient cycle of operation has been achieved.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

I claim:

1. A flash evaporator stage comprising a longitudinally extending hollow housing, first and second end Walls at each end of said housing, a flash box extending between said end walls, said flash box having spaced side walls, a pair of liquid separating walls extending from said first end wall adjacent the top of said flash box to said second end wall adjacent the bottom of said flash box to form unflashed liquid compartments below said liquid separating walls and flashed liquid compartments above said walls, said liquid separating walls extending outwardly from said spaced side walls, said unflashed liquid compartments being in flow communication with the interior of said flash box along the length thereof, said first end wall having an opening therein below said liquid separating Walls on either outward-side of said flash box side walls, said second end wall having openings therein above said liquid separating walls on either outward side of said flash box side walls, said second end wall openings extending upward to a point below the top edge of said flash box side walls.

2. The flash evaporator stage of claim 1 including condenser means in said housing spaced above said flashed liquid compartments, and vapor-liquid deflector means located above said flash box along the length thereof, said vapor'liquid deflector means being operative to deflect a vapor-liquid mixture rising from said flash box into said flashed liquid compartments.

3.'The flash evaporator stage of claim 2 including liquid-vapor separating means, said liquid-vapor separating means being mounted in said housing between said condenser means and said flashed liquid compartments, said liquid-vapor separating means isolating said condenser means from said flashed liquid compartments whereby liquid will be trapped by said liquid-vapor separating means and only vapors can reach said condenser means.

4. The flash evaporator stage of claim 1 including valve means, said valve means being mounted in said flash box along the length thereof to control the flow area of fluid in said flash box and thereby control the pressure on said fluid.

5. The flash evaporator stage of claim 2 including distillate collector means, said distillate collector means being mounted below said condenser means to collect condensed vapors from said condenser means, said distillate collector means including a distillate receiving tank located in said housing below said flash box, said distillate receiving tank being in communication with said collector means.

6. The flash evaporator stage of claim 5 wherein said distillate receiving tank has end walls, said tank end walls having low level openings therein adjacent the bottom edge thereof, and at least one distillate separating wall spaced from and parallel to one of said tank end walls, said distillate separating wall extending upward from the bottom of said tank to a higher level than said lastmentioned tank end wall openings, said distillate separating wall extending the length of said last-mentioned tank end wall openings.

7. The flash evaporator state of claim 1 including a second flash box extending between said end walls parallel to said first flash box, said second flash box having its upper edge in the same plane as the upper edge of said first-mentioned flash box, one of said pair of liquid separating walls extending between one side wall of said first-mentioned flash box and an adjacent side wall of said second flash box, said unflashed liquid compartment below said one liquid separating wall being in flow communication with the interior of said second flash box along the length thereof, one of said first and one of said second end wall openings being spaced between said firstmentioned and second flash boxes, said last-mentioned openings having a width equal to the width of said one liquid separating wall.

8. A multi-stage flash evaporator comprising a longitudinally extending hollow housing, first, second and third end walls equallyrspaced along the length of said housing and perpendicular to the axis thereof, a first flash box extending between said first and second end walls, a second flash box extending between said second and third end walls axially in line with said first flash box, said first and second flash boxes having spaced side walls, first liquid separating walls extending from said first end walls adjacent the top of said first flash box to said second end wall adjacent the bottom of said first flash box to form first unflashed liquid compartments below said first liquid separating walls and first flashed liquid compartments above said first liquid separating walls, second liquid separating walls extending from said second end wall adjacent the top of said second flash box to said third end wall adjacent the bottom of said second flash box to form second unflashed liquid compartments below said second liquid separating walls and second flashed liquid compartments above said second liquid separating walls, said unflashed liquid compartments being in flow communication with the interior of their respective flash boxes along the length thereof, said first, second and third end walls having openings therein, said end wall openings being only in communication with said flashed and unflashed liquid compartments.

9. The multi-stage flash evaporator of claim 8 including condenser means mounted above said flashed liquid compartments, said condenser means including liquid conduits extending through said first, second and third end walls, brine supply means for supplying brine through said first end wall openings, condenser brine supply means for supplying brine through said condenser conduits from said third end wall toward said first end wall, said brine supply means supplying brine at a temperature slightly higher than the temperature of brine supplied by said condenser brine supply means.

ll). The multi-stage flash evaporator of claim 9 including distillate collecting means, said distillate collecting means being mounted below said condenser means, said distillate collecting means including a first distillate collector between said first and second end walls and a second distillate collector between said second and third end walls, a distillate tank extending between said first and third end walls .and in communication with said first and second distillate collectors, said distillate tank having at least one Wall therebetween dividing said tank into a first and second chamber, said first distillate chamber being in vapor communication only with said first distillate collector, said second distillate chamber being only in vapor communication with said second distillate collector, said first and second distillate chambers being in liquid flow communication with each other.

11. The multi-stage flash evaporator of claim 16 wherein said distillate tank separator wall has a low level opening along the bottom edge thereof and below the level of distillate in said distillate tank, and a distillate separating wall spaced from said distillate tank separating wall extending the length of said tank separating wall opening, said distillate separating wall extending upward to a level higher than the upper level of said distillate tank separating wall opening.

12. The multi-stage flash evaporator of claim 9 wherein said brine supply means includes feedback means for feeding brine passing through said condenser conduits and out said third end wall to said first end wall openings, said condenser brine supply means including means for supplying brine from said third end wall openings into said first end wall condenser conduits.

13. The multistage flash evaporator of claim 1 2 wherein said feedback means includes means for supplying a predetermined amount of heat to said brine before supplying said brine to said first end wall openings, and heat dissipating means for removing said predetermined amount of heat from said brine before said brine is re turned to said feedback means.

14. The multi-stage flash evaporator of claim 13 ineluding valve means in at least one of said flash boxes, said valve means being operative to control the fluid flow area of said last-mentioned flash box and thereby control the flow of fluid in said flash box.

15. The multi-stage flash evaporator of claim 9 including liquid-vapor deflectors, said liquid-vapor deflectors being spaced above said flash boxes between said end walls, said liquid-vapor deflectors being operative to deflect .a vapor-liquid mixture rising over the walls of said flash boxes into said flashed liquid compartments.

16. The multi-stage flash evaporator of claim 15 wherein said liquid-vapor deflectors have an arcuate cross section, two of said deflectors being provided in back-to-back relationship between said end walls and centrally of said flash box side walls.

17. A multi-stage flash evaporator comprising a longitudinally extending hollow housing, first, second and third end walls equally spaced along the length of said housing, a first group of flash boxes extending between said first and second end walls, said first group of flash boxes being parallel one to another, a second group of flash boxes extending between said second and third walls, said first and second groups of flash boxes being equal in num her with each flash box in said first group being axially aligned with a flash box in said second group, said first and second groups of flash boxes having their top edges in the same plane, a first group of liquid separating walls extending from said first end walls adjacent the top edges of said first group of flash boxes to said second end wall adjacent the bottom of said flash boxes, said first group of liquid separating walls extending between each of said flash boxes, a second group of liquid separating walls extending from said second end walls adjacent the tops of said second group of flash boxes to said third end walls adjacent the bottom edges of said second group of flash boxes, said second group of liquid separating walls extending between each of said second group of flash boxes, said liquid separating walls forming unflashed liquid compartments below said liquid separating walls and flashed liquid compartments above said liquid separating walls, said unflashed liquid compartments being in flow communication with the interiors of said flash boxes along the lengths thereof, said first and second and third end walls having openings therein only in communication with each of said flashed and unflashed liquid compartments.

18. The multi-stage flash evaporator of claim 17 including a centrally disposed condense-r extending between said first, second and third end walls along the length of said housing, said condenser being mounted above said flash boxes, liquid-vapor deflectors extending the length of sad flash boxes above said flash boxes, said liquidvapor deflectors being operative to deflect liquid into said flashed liquid compartments, and liquid-vapor separators extending between saidfirst, second and third end walls, said liquid-vapor separators being mounted on opposite sides or" said centrally located condenser to isolate said condenser from liquid in said housing, said liquid-vapor separators being operative to separate liquid from liquid- 1 1 vapor mixtures and allow vapor to reach said condenser to be condensed into distillate thereby.

19. The multi-stage flash evaporator comprising-a plurality of stages, end walls for each stage separating eachstage from every other stage, a group of parallel spaced flash boxes extending between the end walls of each stage, flash boxes in each group being equal in number and spaced in the same manner as the flash boxes in every other group, liquid separating walls extending between the end walls 'in each stage and between adjacent flash boxes, said liquid separating walls extending from one end wall adjacent the top edge of its associated flash box to the other end \wall adjacent the bottom edge of its associated flash box, said liquid separating walls forming unflashed liquid compartments below said liquid separata ing walls and flashed liquid compartments above said liquid separating walls, said unfl-ashed liquid compartments being in flow communication with the interiors of said flash boxes along the length thereof, said end walls having openings therein only in communication with each of c said flashed and unflashed liquid compartments.

20. The multi-stage flash evaporator of claim 19 including a centrally disposed condenser extending between the end. walls of each of said stages above said flash boxes, liquid vapor deflectors extending the length of said flash boxes above each of said flash boxes, said liquid vapor deflectors being operative to deflectliquid into said flashed liquid compartments from said flash boxes.

References Cited by the Examiner UNITED STATES PATENTS 2,934,477 4/60 Siegfried 2O2-1 74 3,003,931 10/ 61 Worthen et a1 202-205 X 3,142,381 7/61 Ris et a1 202173 3,146,177 8/ 64- Chalmers et al 202l73 X 3,174,914- 3/65 Worthen et a1, 20220S X NORMAN YUDKOFF, Primary Examiner. 

1. A FLASH EVAPORATOR STAGE COMPRISING A LONGITUDINALLY EXTENDING HOLLOW HOUSING, FIRST AND SECOND END WALLS AT EACH END OF SAID HOUSING, A FLASH BOX EXTENDING BETWEEN SAID END WALLS, SAID FLASH BOX HAVING SPACED WIDE WALLS, A PAIR OF LIQUID SEPARATING WALLS EXTENDING FROM SAID FIRST END WALL ADJACENT THE TOP OF THE SAID FLASH BOX TO SAID SECOND END WALL ADJACENT THE BOTTOM OF SAID FLASH BOX TO FORM UNFLASED LIQUID COMPARTMENTS BELOW SAID LIQUID SEPARATING WALLS AND FLASHED LIQUID COMPARTMENTS ABOVE SAID WALLS, SAID LIQUID SEPARATING WALLS EXTGENDING OUTWARDLY FROM SAID SPACE SIDE WALLS, SAID UNFLASHED LIQUID COMPARTMENTS BEING IN FLOW COMMUNICATION WITH THE INTERIOR OF SAID FLASH BOX ALONG THE LENGTH THEREOF, SAID FIRST END WALL HAVING AN OPENING THEREIN BELOW SAID LIQUID SEPARATING WALLS ON EITHER OUTWARD SIDE OF SAID FLASH BOX SIDE WALLS, SAID SECOND END WALL HAVING OPEINING THEREIN ABOVE SAID LIQUID SEPARATING WALLS ON EITHER OUTWARD SIDE OF SAID FLASH BOX SIDE WALLS, SAID SECOND END WALL OPENINGS EXTENDING UPWARD TO A POINT BELOW THE TOP EDGE OF SAID FLASH BOX SIDE WALLS. 